Greaseproof coating composition and product



Unite States Patent 3,030,323 GREASEPROOF COATING COMPOSITION AND PRODUCT Leslie L. Turai, Loudonville, N.Y., assignor to West Virginia Pulp and Paper Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 6, 1959, Ser. No. 851,234 10 Claims. (Cl. 260-285) My present invention relates to improvements in coating compositions for paper and thelike, especially for rendering the coated paper grease and water resistant; and to the product so treated. It is a principal object of my invention'to devise an effective coating composition which when applied to-paper and the like, will give it a high grease and water resistance and one-that will be free of the unwanted property of blocking, ie, the tendency of two coated sheets to stick together at relatively low temperatures.

In the course of experimentation with various coating materials, it was found that a water emulsion of the copolymer of vinyl acetate and dibutyl maleate, which has a relatively low viscosity at high solids, resulted, when applied to paper or paperboard, in a coat of good grease resistance and flexibility, but one that exhibited blocking. On the other hand, polyvinyl alcohol (PVAl) used in water solution as a coating for paper and applied in a substantial coat weight, also imparted a high degree of grease resistance, but the coating was brittle and the high viscosity of the PVAl solution itself resulted in films that were either too thin, or if applied in sufiicient thickness, were difiicult to dry. I have now discovered that by properly combining the two polymers, coating compositions are to be had having reasonably high solids at workable viscosities, and when applied to paper and the like result in improved grease and water resistance without undue blocking. In general, it was found that the optimum ratios of the copolymer ranged from 80 parts copolymerzZO parts PVAl to 50 parts copolymer:50 parts PVAl. I have further found that an even less blocking effect is to be had by the incorporation in the mixture of finely divided fillers such for example as clay, talc, titanium dioxide and others. I'have also found that clay and other fillers have the further property, when present, of facilitating the drying of the coated sheet by enabling it ,to'be passed around heated drum driers, as for example, those comprising the drying unit of a Fourdrinier papermaking machine. When clay or other filler is not present, it has been found advisable to dry the coated paper by the-use of warm air, in a manner similar. to the drying of other off-the-machine coated papers.

The improved coating composition is applied to the paper, preferably by means 'of a coating device of the type known in the art as a trailing blade coater, in which a pool of the coating composition'is'maintained in the bight between a backing roll aroundwhich the paper travels, and a flexible blade, one end of which extends close to the paper. on the backing roil and meters the flow of the coating composition to the paper.

Since it is difiicult to get an entirely pinhole-free first coat, two or more coats are recommended. Study and inspection of the coated sheets indicate that the first coating serves to -fill up minute irregularities in the web surface, and provides a relatively smooth foundation for the second coat.

My invention will be further understood by reference to the following examples:

Example 1 40 parts by weight of Elvanol 70-05 (a fully hydrolyzed polyvinyl alcohol of low viscosity-4 to 6 centipoises-as measured by the Hoeppler' falling ball method using a 4% water solution at 20 C., such compound being manufactured by E. I. du Pont de Nemours & Company, Inc., of Wilmington, Del.) is dispersed in 160 parts by weight of cold water; then the temperature of the mixture is raised to 200 F. under good agitation and maintained at that temperature for approximately one hour. After all the polyvinyl alcohol has dissolved, the mixture is cooled to 130 F. and parts by weight (based on resin solids) of Everflex A (a polyvinyl acetate dibutyl maleate copolymer, water emulsion manufactured by the Dewey and Almy Chemical Division of W. R. Grace"& Company, Cambridge, Mass, and having a viscosity of from 1000 to 1400 cps. at 25 C. Brookfield #3 Spindle 60 r.p.m.') is added. Finally, the solid content of the mixture is adjusted by the addition of water to the desired level, for example, to a level of approximately 33% solids for trailing blade coating and to approximately 20% solids for air knife coating.

Example 2 Composition similarly prepared as in Example 1, but containing 50 parts of Elvanol -05 and 50 parts of Everflex A emulsion (based on resin solids).

Example 3 5' parts by weight of Elvanol 52-22 (a medium-viscosity, 86-89% hydrolyzed polyvinyl alcohol, manufactured by E. I. du Pont de Nemours & Company, Inc., having a viscosity of 21-25 measured the same as for Elvanol 70-05) is dispers'edin 175 parts by weight of cold water; then the temperature of the mixture is raised to 190 F. under good agitation and held there until all the polyvinyl alcohol has dissolved. Then the mixture is cooled to 130 F. and parts by weight (based on resin solids) of Everflex A emulsion is added. Then the solid content of the mixture is adjusted by the addition of water to approximately 30% for trailing blade coating and to approximately 18% for air knife coating. No filler is added.

Example 4 15 parts by weight Elvanol 70-05 is dispersed in 160 parts by weight of cold water; the temperature is then raised to 200 F. with agitation and maintained at that temperature for approximately one hour. After all the polyvinyl alcohol has dissolved, the mixture is cooled to F. and 60 parts by weight of EverflexA is added, followed by the addition of 25 parts by weight of clay. Water isthen added to bring the solids to the desired level, as mentioned in Example 1.

Polyvinyl alcohol is manufactured by the hydrolysis of polyvinyl acetate. For the practice of the invention, it is preferred to use a polyvinyl alcohol which has a degree of hydrolysis of at least 75% and a viscosity not exceeding 30 centipoises when it is measured as a 4% solution in water at 20 C. by means of the Hoeppler fallingball method; that is a low or medium viscosity type polyvinyl alcohol.

The polyvinyl acetate-dibutyl maleate copolymer emulsion is well disclosed in the patent literature, an example being Patent 2,833,737 of May 6, 1958, issued to W. R. Grace and Company, and can be referred to for a more complete disclosure of Everflex A. This substance is the copolymer per se without the addition of hexylene or other glycol as set forth in the patent. As stated, the monomer mixture to be emulsion polymerized contains from 17 /2 to 32 /2% dibutyl maleate, and 82 /2 to 67 /2 polyvinyl acetate. In forming the improved coating composition, other maleate esters may be used in emulsion form, i.e.; diethyl maleate (diethyl butenedioate); diisopropyl maleate (diisopropyl butenedioate); di(methyl 3 amyl) maleate (di-l, 4-dimethyl-l-butyl butenedioate); and di-2-ethyl-hexyl maleate (di-Z-ethyl-hexyl butenedioate) and the corresponding fumarates.

Various additives may also be incorporated in my improved coating composition; for example, defoamers; wax emulsions of various types, including paraffin wax. The latter is particularly valuable when the coated paper is dried upon a drum type of drier, since it facilitates the release of the coated surface from the drying surface.

The improved coating compositions described in Examples 1 and 2 were applied on bleached food board of approximately fourteen caliper point thickness by a trailing blade coater in two coating applications. The result-. ing board was tested for grease resistance, water penetra- Nine out of ten samples showed no turpentine penetration after 160 hours of testing, when the test was abandoned.

Several specimens showed no water penetration at the end of 168 hours when the test was abandoned.

The grease tests are made on specimens of circular shape of 3-inch diameter, and conducted according to the TAPPI turpentine test T454m-44, with the following modifications:

(1) The average obtained from ten specimens is used for each test, instead of the 30 specified;

(2) The tests are continued until failure occurs, instead of the 60 minutes specified by TAPPI.

(3) Due to the longer duration of the tests, the turpentine is replenished every 24 hours and an inverted bottle is placed over the samples to reduce turpentine evaporation.

The water penetration tests are conducted as follows: Specimens of 2 x 2 inches in size are floated on dyed water, the coated side contacting the Water. The time required for the first spot of dye to ShOW through the opposite side of the specimen is recorded. The average time obtained on five specimens is used for each test.

The blocking tests are carried out as follows: Specimens of the coated paper are placed face to face, and face to back under pressure of one pound per square inch by the action of a metal block placed thereon. They are then heated to 180 F. and such temperature maintained for 16 hours, when the specimens are then separated. No damage to the surface should be observed. Coated paper made as per the foregoing examples satisfactorily passed this test.

While certain preferred embodiments of the invention have been illustrated and described in detail, it is to be understood that changes may be made therein and the invention practiced in other forms. It is not therefore, the intention to limit the patent to the specific examples illustratively described, but to cover the invention broadly in whatever form its principles may be utilized.

Throughout the specification the term maleate is used rather than butenedioate, such term being also intended to cover the trans (i.e., the fumarates) as well as the cis compounds (the maleates).

I claim:

1. A composition yielding a flexible plastic coating when applied to paper or paperboard, such coating exhibiting the property of non-blocking at 180 F., said composition comprising in combination an aqueous dispersion of the copolymer formed by the emulsion copolymerization of vinyl acetate and dialkyl maleate selected from the group consisting of diethylmaleate, diisopropylmaleate, dibutyl maleate, dimethylamyl maleate, di-2- ethyl hexyl maleate and the corresponding fumarates; and an aqueous solution of low to medium viscosity types polyvinyl alcohol having a degree of hydrolysis of at least the said ingredients being present in the proportion of to 50 parts by Weight of copolymer resin and 20 to 50 parts by weight of polyvinyl alcohol.

2. Paper or paperboard coated with a flexible film of plastic composition defined in claim 1, and exhibiting valuable grease-and-waterproof properties.

3. A composition yielding a flexible plastic coating when applied to paper and paperboard, such coating exhibiting the property of non-blocking at F., said composition comprising in combination an aqueous dispersion of the copolymer formed by the emulsion copoly merization' of vinyl acetate and dibutyl maleate and an aqueous solution of low to medium viscosity types polyvinyl alcohol, having a degree of hydrolysis of at least 75%, the said ingredients being present in the proportion of 80 to 50 parts by weight of the copolymer and 20 to 50 parts by weight of polyvinyl alcohol.

4. Paper or paperboard coated with a flexible film of plastic composition defined in claim 3, and exhibiting valuable grease-and-waterproof properties.

5. A composition yielding a flexible plastic coating whenapptlied to paper and paperboard, such coating exhibiting the property of non-blocking at 180 F., said composition comprising in combination an aqueous dispersion of the copolymer formed by the emulsion copolyw merization of vinyl acetate and dibutyl maleate and an aqueous solution of low to medium viscosity types polyvinyl alcohol, having a degree of hydrolysis of at least 75%, the said ingredients being present in the proportion of 80 to 50 parts by Weight of the copolymer and 20 to 50 parts by weight of polyvinyl alcohol together with at least one additive chosen from the group clay, talc, titanium dioxide.

6. Paper or paperboard coated with a flexible film of plastic composition defined in claim 5, and exhibiting valuable grease-and-waterproof properties.

7. The composition according to claim 5, additioned by paraffin wax.

8. Paper or paperboard coated with a flexible film of plastic composition defined in claim 7, and exhibiting valuable grease-and-waterproof properties. 7

9. The composition according to claim 5 containing said ingredients in the following proportions:

Vinyl acetate, dibutyl maleate copolymer 60 Polyvinyl alcohol 15 Clay 25 10. Paper or paperboard coated with a flexible film of plastic composition defined in claim 9, and exhibiting valuable grease-and-waterproof properties.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. $030,323 April 1'7, 1962 Leslie L. Turai It is hereby certified that error appears in the above numbered petant requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 27, for "5" read 25 Signed and sealed this 28th day of August 1962.

(SEAL) Atteet:

ESTON GD JOHNSON DAVID L, LADD 

1. A COMPOSITION YIELDING A FLEXIBLE PLASTIC COATING WHEN APPLIED TO PAPER OR PAPERBOARD, SUCH COATING EXHIBITING THE PROPERTY OF NON-BLOCKING AT 180*F., SAID COMPOSITION COMPRISING IN COMBINATION AN AQUEOUS DISPERSION OF THE COPOLYMER FORMED BY TEH EMULSION COPOLMERIZATION OF VINYL ACETATE AND DIALKYL MALEATE SELECTED FROM THE GROUP CONSISTING OF OF DIETHYLALEATE, DIISOPROPLYFROM THE GROUP CONSISTING OF DIMETHYLAMYL MALEATE, DI-2ETHYL HEXYL MALEATE AND THE CORRESPONDING FUMARATES; AND AN AQUEOUS SOLUTION OF LOW TO MEDIUM VISCOSITY TYPES POLYVINYL ALCOHOL HAVING A DEGREE OF HYDROLYSIS OF AT LEAST 75%, THE SAID INGREDIENTS BEING PRESENT IN THE PROPORTION OF 80 TO 50 PARTS BY WEIGHT OF COPOLYMER RESIN AND 20 TO 50 PARTS BY WEIGHT OF POLYVINYL ALCOHOL. 